A security barrier or bollard may be used for resisting an unauthorised passage of a vehicle such as a car or lorry. Such barriers typically comprise a housing with a barrier member mounted to it. The housing is typically cast into concrete foundations below ground level. The bather member is arranged to be retractable so that it can be stowed within the housing to allow the vehicle to pass, or deployed to a working position above ground level to prevent or inhibit the vehicle to pass. In the deployed position the barrier member is required to be sufficiently high above ground level to prevent or inhibit the vehicle from passing.
Security bathers are typically provided in two categories. The first category is a high security barrier, or anti-terrorist barrier, that is intended to prevent a vehicle from passing. Such a barrier is robustly constructed and is typically about 1-1.5 meters above ground level. A high security barrier might be used at a road entrance to an airport or an official building, such as a Government building, and is typically able to withstand a crash impact from a car or lorry. The second category of security barrier might be used at a home or work premises to safeguard a car parking space or driveway from being used by another vehicle. Such barriers are relatively less robustly constructed, and may extend up to one meter above ground level.
It is known to provide a security barrier which comprises a wedge-shaped barrier member which is arranged to pivot substantially at ground level about the thin end of the wedge. The barrier member is typically the width of a road and is operable to be stowed in a housing in the ground so that a surface of the wedge is level with the ground. The security member may be deployed above ground so that an uppermost part of the wedge is up to a height of 1.5 meters. Such a security barrier has the problem that when the wedge is stowed in the ground, a deep foundation is required to be used for the housing. It will be appreciated that the depth of the foundation must be at least as deep as the height that the wedge-shape barrier member protrudes from the ground when in the deployed position. Using such a deep foundation is disadvantageous, particularly in an urban environment, because it may interfere with services such as power lines, drains, or communication cables.
In another known arrangement the barrier member comprises a rectangular flat plate having a skirt or bellows. The flat plate is arranged to pivot at ground level about one edge, and the skirt extends between the other three edges of the flat plate and the ground. A problem with such an arrangement is that the flat plate forms an overhang above ground which may represent a safety hazard due to the proximity of the ground as the flat plate moves back to the stowed position.
It is also known to provide a security bollard or post which is moveable between a vertical position above ground and a vertical position below ground. Such an arrangement also has the problem of requiring a deep foundation for a housing for the post, which must be at least as deep as the height of the bollard above ground. In an alternative arrangement the post is telescopic so that the foundations for the housing are not required to be as deep, but such a telescopic post adds cost and complexity. Such security bollards or posts generally represent less of a safety hazard than the flat plate security barrier due to the closer fitment of the bollard or post relative to the ground.
It is further known to provide a security bollard or post which is pivotable below ground level. The post is mounted in a housing having a flap which must be opened before the post can be deployed. Once the post has been deployed the flap must be closed to present a flat surface at ground level for safety reasons. Such arrangements require a relatively shallow foundation for the housing, but have the disadvantage that an additional step of opening the flap is required to deploy the post and to create a flat surface after the post has been deployed. Such arrangements also add cost and complexity.
It is broadly an object of the present invention to address one or more of the above mentioned disadvantages of previously known security barriers.